When you know where you are going, it makes it somewhat easier to stay on course. I wouldn't take a drastic turn towards the east if I knew I wanted to be moving south. This is why it's so vital that we have some vision for our lives.
This doesn't mean that we need to have every step clearly defined and determined for our future, but that we make choices with a destination in mind. With this focus we will grow increasingly cognizant of what might distract us from our true purpose and keep our focus where it belongs.
A person who is dedicated to fulfilling their vision will refuse to make decisions that might hinder their journey. It's a key part of personal vision casting to define our ambitions and practice the behaviors to help make it a reality.